Should I tell on a cheating spouse?

[NessaVanessa]

Went out Friday night with some friends to a club in London. I have a friend called J - Not childhood friend, but we are friendly enough, we know each other as our DC are going to the same school. J has a spouse - M - who I saw in the same club with a small group, don't know if it's friends or coworkers, doesn't matter. M did not see me. Most of their group left after a drink but I did see long, handsy snogging between M and the only other person that stayed. At one point I thought they left because they disappeared but then walked back from where the toilets are. Ew. I am not saying something happened in there, but I wouldn't be surprised either.
I know J loves M and it would be heartbreaking to learn. They have two kids, I thought they are super in love. So I don't know what to do.
Should I tell J what I've seen M doing? I took a few blurry videos from a distance. You can imagine it's not great quality, but I think M is recognisable if you are familiar.
What would you do?
(edit: Name changed)

Oh i just assumed it was the man, sorry. Im not sure then. He or she might think you had a malicious interest ie to split them up because you fancied him.

I was the wife at home with the children. When I was told my life fell apart but I now see that I had to be told as my children and I were living a lie, and the that lie was doing us a lot of damage. The wife deserves to know who she is living with.

I would tell her

him.
The cheater is the wife.

Sorry yes tell him - as a friend, absolutely. Why wouldn’t you?

It's very easy to set up a throwaway anon email. Set one up and send the videos to J. Then wait to hear from J about what M's been up to.

Yes correct. It’s not her circus, not her monkeys.

Last week I mustered up the courage to just talk to him. I volunteered at my kids' school to be one of the parents who go for a woodland walk with the two classes, and he was there, too. I didn't know he was going to be there. I felt this is a sign to just do it. Obviously I didn't just walk up to him or broadcast it over the groups of kids. There was a moment where parents were just minding their business when we reached a play area and the kids were just doing their their thing. He was on the side, checking work emails, so I walked up to him and just blurted out that I needed to talk to him about something. Not too original. He asked if everything is ok, if it is about the kids and I said told him no. So we agreed to wait outside the school when we walked the kids back. All the other parents ran off so we got coffee and just talked. I told him that it is about M. He immediately went god, what did she do? I told him I am not sure, but I saw her in London on Friday. So then, I told him what I saw, pretty much everything in my original post. He was trying to find ways that could convince him otherwise, asked questions what she was wearing, about this other person, etc, and everything seemed to check out. He even had a good idea who she was with. Work 'bestie'. He joked that he would have needed something stronger than coffee for this. He thanked me for my honesty. We never even had to talk about the videos.

This was last week. Over the weekend I got some some WhatsApp messages from him. He confronted her about this. M didn't try to deny it, her defence was that she only cheated with other women and not men so hopefully J could see past this, and it doesn't mean that she doesn't love him. He is not going to, he has an old flat he inherited from his grandad a while ago, so for the time being he will go there. He will look into the divorce but it is a lot now. Especially with half term. There are places they wanted to go as a family, and they will still take the kids. Now he's trying to work out a way to tell the kids that they will be separating. M doesn't want that. She wants to stay together for the kids and try to fix it. I didn't say anything to this, I don't want to influence anyone, but I don't think something like this can be fixed. I am so hopeful he will come out happy from this.

It sounds like you handled a tricky conversation very well. It's all well and good M saying she wants to fix it but maybe she should have thought about that before cheating.